On 03/06/2020 03:33 PM, William Morgan wrote:

I tried re-add and I get the following error:

bill@bill-desk:~$ sudo mdadm /dev/md0 --re-add /dev/sdl1
mdadm: Cannot open /dev/sdl1: Device or resource busy

sdl is not mounted, and it doesn't seem to be a device mapper issue:

  cat /proc/mdstat  and/or cat /proc/partitions

  and see if the disk was brought up as an array of its own (something like
/dev/md127, etc..), If so, simply

  sudo mdadm --stop /dev/md127

  The try you re-add again. I recently had that occur when I put in a
replacement disk for a raid1 array. Even though I just cut the plastic
anti-static bag off the brand-new drive, when I booted the system, it came up
as an array (of what I don't know). I got the same device busy and simply used
--stop on the obviously not-an-array array, The --re-add worked just fine
afterwards.

-- 
David C. Rankin, J.D.,P.E.